A pulse-pumped passively Q-switched laser with controllable optical delay

Abstract

The present invention discloses a pulse-pumped passive Q-switched laser with a controllable optical delay, which mainly adds a photoelectric monitoring and feedback function to the pulse-pumped passive Q-switched laser, monitors the light delay in real time through a photoelectric detector, compares the test value with a preset value through a feedback device, and adjusts the pump power through feedback, so that the optical delay of the laser is stabilized near the preset value. The scheme of the present invention can effectively control the optical delay of the pulse-pumped passive Q-switched laser, improve the delay stability of the passive Q-switched laser, and synchronize the optical pulse with an external device or apparatus, etc., and expand the application of the passive Q-switched laser in the fields of laser radar, spectral instruments, photoelectric detection, etc.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a pulse-pumped passive Q-switched laser with a controllable optical delay function. Background Art

[0002] Q-switching technology is the main technology for obtaining giant pulse lasers. There are two types of Q-switching technology: active Q-switching and passive Q-switching. Compared with active Q-switching technology, passive Q-switching technology has the characteristics of compact structure, high energy conversion efficiency, and low price. It has broad application prospects in military and civilian fields such as long-distance measurement, remote sensing detection, medical health, and space communications, and has occupied an increasingly important position.

[0003] Cr 4+ :YAG saturable absorption Q-switching is the most widely used type of passive Q-switching. 4+ : When the incident light signal is weak in the absorption band of the YAG crystal, it will show a very obvious absorption trend for the incident light; when the incident signal is enhanced to a certain extent, it will suddenly show an obvious absorption saturation trend for the incident light. 4+ :The sudden absorption saturation characteristics of the YAG crystal allow it to be placed in the resonant cavity as a Q switch for passive Q modulation.

[0004] By Cr 4+ : The principle of YAG saturable absorption passive Q switching shows that the generation of its laser pulse is mainly affected by the pump power, resonant cavity and Cr 4+ : The influence of YAG crystal. When the laser is debugged, its resonant cavity and Cr 4+ : Once the parameters of the YAG crystal are determined, the pump power plays an important role in the generation of pulses. Especially in the continuously pumped passive Q-switched laser, if the pump power is not actively controlled, the moment and repetition frequency of the pulse generation will always be unstable. This instability causes the optical pulses of the passive Q-switched laser to be unable to synchronize with other instruments or detection equipment, which greatly limits the application scope of the passive Q-switched laser. This method of controlling the laser pulse by pulse pumping allows the optical pulse repetition frequency to be the same as the pulse pump electrical signal repetition frequency, which improves the stability of the optical pulse repetition frequency to a certain extent. However, the fluctuation of the ambient temperature and the pulse generation conditions makes the moment of the pulse generated by the passive Q-switched method of pulse pumping relative to the pulse pump electrical signal still have great uncertainty, that is, the optical delay fluctuation range is large. This disadvantage greatly limits the application scope of passive Q-switched lasers. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the present invention proposes a pulse-pumped passively Q-switched laser with a controllable optical delay function. The laser can effectively control the optical delay of the pulse-pumped passively Q-switched laser, improve the delay stability of the passively Q-switched laser, and at the same time synchronize the optical pulse with an external device or apparatus, thereby expanding the application of the passively Q-switched laser in the fields of lidar, spectroscopic instruments, photoelectric detection, etc.

[0006] The technical solution adopted by the present invention is:

[0007] A pulse-pumped passively Q-switched laser with a controllable optical delay function. The laser places an optical detector with a feedback device in the pulse-pumped passively Q-switched laser, detects the delay of the optical pulse relative to the rising edge of the pulse pumping electrical signal in real time and compares it with a preset value. When a deviation occurs in the return signal, an instruction is issued to adjust the low level of the pulse pumping electrical signal accordingly, so as to stabilize the pulse optical delay of the pulse-pumped passively Q-switched laser.

[0008] The specific technical solutions of the present invention are as follows:

[0009] The invention provides a pulse pumped passive Q-switched laser with a controllable optical delay function. The laser comprises: a pump source, a coupling lens, a laser gain medium with a total reflection film, a passive Q-switched crystal, an output mirror, a beam splitter, a light detector and a feedback device, wherein: the pump source, the coupling lens, the laser gain medium with a total reflection film, the passive Q-switched crystal, the output mirror and the beam splitter are arranged in sequence according to optical coaxiality; the light detector is arranged corresponding to the beam splitter to monitor the light reflected by the beam splitter in real time; the feedback device is arranged between the light detector and the pump source, and adjusts the power of the pump source according to the result detected by the photoelectric detector.

[0010] The pump source adopts a pulse operation mode;

[0011] The laser gain medium with the total reflection film and the output mirror form a resonant cavity;

[0012] The pump source converges the pump light onto the laser gain medium with a total reflection film through a coupling lens. After the gain medium 3 absorbs the pump light, a population inversion is formed, and the laser generates gain.

[0013] The passive Q-switched crystal is a Q-switch based on the saturable absorption characteristics of the crystal;

[0014] The passive Q-switched crystal can adjust the loss in the resonant cavity, and when the gain in the laser is greater than the loss, the generated pulse light is output from the output mirror;

[0015] The beam splitter splits a part of the output pulse light to the light detector;

[0016] The light detector receives a portion of the light split by the beam splitter and transmits the monitoring result to the feedback device;

[0017] Optionally, the pump source is a semiconductor laser with direct output, and the wavelength corresponds to the absorption peak of the laser gain medium with the total reflection film;

[0018] Optionally, the beam splitter is an optical lens with partial reflectivity for the output light wavelength;

[0019] Optionally, one side of the surface of the laser gain medium with a total reflection film is coated with an anti-reflection film for pump light and a laser high-reflection film, and the other side is coated with an anti-reflection film for fundamental frequency light.

[0020] Optionally, the output mirror is a plano-concave mirror, and a fundamental frequency light partial transmission film is coated on the side facing the laser gain medium with the total reflection film.

[0021] Optionally, the light detector is a photodiode, which is a semiconductor device that can respond to a signal in the wavelength range of an output light pulse and convert the light signal into an electrical signal;

[0022] Optionally, the feedback device is a single chip microcomputer, which is a chip that can program logic judgment and instruction programs internally, and can realize the feedback adjustment function of the pulse light delay.

[0023] The advantages and technical effects of the present invention are:

[0024] 1. The present invention adds a light detector to the pulse-pumped passive Q-switched laser. The light detector detects the laser pulse in real time and transmits the information to the feedback device. The feedback device determines the delay of the laser pulse relative to the rising edge of the pulse pump source electrical signal according to the detected signal, automatically adjusts the size of the low level of the pulse pump source, and then adjusts the size of the pulse light delay, so that the light pulse of the pulse-pumped passive Q-switched laser obtains a stable delay.

[0025] 2. The pulse-pumped passively Q-switched laser with controllable optical delay proposed in the present invention can maintain a more stable delay time. This stable delay realizes the synchronization of optical pulses with other devices or instruments, thereby improving the application range of the passively Q-switched laser.

[0026] 3. The present invention achieves the purpose of real-time monitoring of photoelectric delay and adjusting the pre-pump power through a feedback program by adding a light monitoring function to the passive Q-switched laser, thereby realizing a pulse-pumped passive Q-switched laser with controllable photoelectric delay. When the laser is affected by changes in ambient temperature, stress, etc., the pulse-pumped passive Q-switched laser with a controllable light delay proposed by the present invention can maintain a more stable delay time. This stable delay realizes the synchronization of light pulses with other devices or instruments, thereby increasing the application range of the passive Q-switched laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of a pulse-pumped passively Q-switched laser with controllable optical delay function;

[0028] Figure 2 It is the relationship diagram of the pulse laser relative to the square wave delay of the pulse pump source t;

[0029] Figure 3 This is a flow chart for setting square wave parameters of pulse pump source and achieving controllable delay;

[0030] Figure 4 It is the relationship diagram of the pulse laser relative to the square wave of the pulse pump source with a delay of t+△t;

[0031] Figure 5 It is the relationship diagram of the pulse laser relative to the square wave delay of the pulse pump source t-△t;

[0032] Figure numerals: 1. Pump source; 2. Coupling lens; 3. Laser gain medium with total reflection film; 4. Passively Q-switched crystal; 5. Output mirror; 6. Beam splitter; 7. Photodetector; 8. Feedback device. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0034] like Figure 1 As shown: a pulse-pumped passively Q-switched laser with a controllable optical delay device of the present invention comprises a pump source 1, a coupling lens 2, a laser gain medium with a total reflection film 3, a passively Q-switched crystal 4, an output mirror 5, a beam splitter 6, a light detector 7 and a feedback device 8.

[0035] The laser gain medium 3 with the total reflection film and the output mirror 5 constitute a laser resonant cavity.

[0036] The pump source 1 is converged by the coupling lens 2 and absorbed by the laser gain medium 3 with a total reflection film, forming a population inversion in the laser gain medium 3 and causing oscillation in the laser resonant cavity.

[0037] The passive Q-switching crystal 4 is a passive Q-switching crystal based on the saturable absorption characteristics of the crystal and is placed in the laser resonant cavity.

[0038] When the light in the resonant cavity is weak, the passive Q-switched crystal 4 shows a very obvious absorption tendency for light, resulting in a large loss in the resonant cavity, no laser output, and energy accumulation in the laser gain medium; when the light in the resonant cavity is enhanced to a certain extent, the saturable crystal suddenly shows an obvious absorption saturation tendency, and the energy accumulated in the laser gain medium is rapidly released to form a light pulse with a higher peak value.

[0039] like Figure 2 As shown, the pump source 1 pumps the laser gain medium in the form of a pulsed square wave. When the pulsed square wave of the pump source 1 is at a high level, the output power of the pump source 1 is relatively high, so that the gain in the resonant cavity is greater than the loss, and at this time there is a pulsed laser output; when the pulsed square wave of the pump source 1 is at a low level, the output power of the pump source 1 is relatively low, and the loss in the resonant cavity is greater than the gain, and at this time there is no pulsed laser output.

[0040] The level of the pulse square wave of the pump source 1 corresponds linearly to the output size of the pump power. The higher the level, the greater the pump power, and the lower the level, the smaller the pump power. The level of the pump power will affect the delay of the output optical pulse relative to the rising edge of the pump square wave. The higher the pump power, the smaller the delay of the optical pulse; conversely, the smaller the pump power, the greater the delay of the optical pulse.

[0041] The duty cycle of the pulse square wave of the pump source corresponds to the length of the pump power output time. The larger the duty cycle, the longer the pump time, and the more optical pulses can be obtained in one pulse square wave cycle. The frequency of the optical pulse can be made consistent with the frequency of the pulse square wave by adjusting the duty cycle of the pump source pulse square wave, that is, there is only one optical pulse in one pump source pulse square wave.

[0042] The pulse square wave of the pump source 1 needs to set the duty cycle, low level and high level of the pulse pump square wave to appropriate sizes, so that the gain in the laser resonant cavity is greater than the loss and a light pulse is generated at the same time, and the light pulse is delayed by the desired time t relative to the rising edge of the pump square wave. Figure 3 The figure shows the flow chart for setting the parameters of the pump pulse square wave.

[0043] The preset low level of the pulse pump square wave to the appropriate position means that the low level is half of the low level leakage current; there is no pulse laser output at this low level, and there is no pulse laser output when the low level is adjusted within a certain voltage range in both large and small directions, and the delay time of the light pulse relative to the pump light pulse can change linearly with the low level voltage.

[0044] The preset high level of the pulse pump square wave to a suitable position means that after adjusting the low level and duty cycle of the pulse square wave, the high level is adjusted so that the delay time of the optical pulse relative to the rising edge of the pump square wave is the expected value t.

[0045] The preset pulse pump square wave duty cycle is set to an appropriate size, which means that each pulse pump square wave contains only one light pulse, and the duty cycle is set between the output light pulse and the subsequent light pulse. According to this method, the output characteristics of the laser are most stable.

[0046] The photodetector 7 detects the light wave signal in real time, which means that the beam splitter 6 in the laser splits a part of the light in the main light path to the photodetector. In this embodiment, the photodetector is preferably a photodiode, which can convert the received light signal into an electrical signal and transmit the information to the feedback device 8.

[0047] The preferred feedback device 8 in this embodiment adopts a single chip microcomputer, which can perform logical judgment on the pulse delay and then issue a control instruction. Specifically, it is to keep the duty cycle and high level of the pulse pump signal of the laser unchanged at an appropriate position, compare the delay signal tested by the light detector with the set value, and then issue an instruction to the low level of the pulse pump square wave according to the result, so as to realize the feedback adjustment function of the pulse light delay.

[0048] like Figure 4 As shown, the optical detector 7 in the laser detects the light wave signal, and the feedback device 8 compares the delay time of the real-time tested light pulse relative to the rising edge of the pump square wave with the expected value t. When it is judged that the delay time becomes larger than t+△t, the low level of the pulse square wave of the pump source 1 is increased from a to b until the delay time returns to t.

[0049] like Figure 5 As shown, the optical detector 7 in the laser detects the light wave signal, and the feedback device 8 compares the delay time of the real-time tested light pulse relative to the rising edge of the pump square wave with the expected value t. When it is judged that the delay time is reduced to t-△t, the low level of the pulse square wave of the pump source 1 is reduced from a to c until the delay time returns to t.

[0050] In one embodiment of the present invention, the pump source 1 adopts a semiconductor laser with a maximum power of 5W and a central wavelength of 808nm; the coupling lens 2 is a plano-convex mirror with a focal length of f=5mm, and the surface of the plano-convex mirror is coated with an 808nm anti-reflection film with a transmittance greater than 99.5%; the laser gain medium 3 with a total reflection film is a Nd:YAG crystal with a size of φ4×3mm, and the surface close to the coupling lens is coated with an 808nm anti-reflection film with a transmittance greater than 99.5% and a 1064nm high-reflection film with a reflectivity greater than 99.9%, and the other side is coated with a 1064nm high-reflection film with a transmittance greater than 99.9%. .8% 1064nm anti-reflection film; the passive Q-switched crystal 4 is a saturable absorption crystal Cr:YAG, with 1064nm anti-reflection film coated on both sides, a through aperture of 5mm×5mm, and an initial transmittance of 80%; the output mirror 5 is a plano-concave mirror with R=200mm, and a 1064nm partial reflection film with a reflectivity of 85% is coated on the surface; the beam splitter 6 is a plane mirror, and a 45° partial reflection film with a reflectivity of 4% is coated on the surface; the light detector 7 is a photosensitive diode with a through aperture of φ5, which can respond to light of 1064nm wavelength; the feedback device 8 is a single-chip microcomputer.

[0051] In one embodiment of the present invention, a laser gain medium Nd:YAG crystal with a total reflection film absorbs the 808nm pump light emitted by the pump source, and the generated 1064nm light is oscillated through the resonant cavity composed of the end total reflection film and the output mirror of the laser gain medium, and a 1064nm laser pulse is formed through the saturation absorption of the passive Q-switched crystal. A pulse square wave signal with a frequency of 4kHz is applied to the pump source of the passive Q-switched laser, and the expected delay of the light pulse relative to the rising edge of the applied pulse square wave is maintained at 150μs. The low-level leakage current of the tested square wave signal is 3.5A, and the low level of the square wave signal is finally set to half of the leakage current, 1.75A; when the high level of the square wave signal is set to 4.9A, the light pulse delay relative to the rising edge of the applied pulse square wave is the expected value of 150μs; when the duty cycle of the square wave signal is set to 80%, each pulse square wave contains one light pulse, that is, the frequency of the light pulse is consistent with the frequency of the applied square wave signal. After the initial setting is completed, the feedback adjustment function of the microcontroller is turned on to dynamically adjust the low level of the pulse square wave. The optical pulse signal detected in real time by the optical detector is compared with the rising edge of the pulse square wave signal. When the light delay is less than 150μs, the level is reduced until the light delay is equal to 150μs. When the light delay is greater than 150μs, the low level is increased until the light delay is equal to 150μs. Through such feedback adjustment, the light delay is maintained at 150μs.

[0052] As can be seen from the above, the present invention achieves the purpose of real-time monitoring of light output delay and adjusting the pre-pump power through a feedback program by adding a light monitoring function to the passive Q-switched laser, thereby realizing a pulse-pumped passive Q-switched laser with controllable light output delay. When the laser is affected by changes in ambient temperature, stress, etc., the pulse-pumped passive Q-switched laser with a controllable light delay proposed by the present invention can maintain a more stable delay time. This stable delay realizes the synchronization of light pulses with other devices or instruments, thereby increasing the application range of the passive Q-switched laser.

[0053] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, those skilled in the art should understand that the scope of protection of the present invention is not limited to the above-mentioned preferred embodiments, and various changes made to the present invention in form and detail are all within the scope of protection of the present invention.

Claims

1. A pulse light delay feedback adjustment method for a pulse pumped passively Q-switched laser with a controllable light delay, characterized in that: The pulse pumped passive Q-switched laser comprises: a pump source (1), a coupling lens (2), a laser gain medium with a total reflection film (3), a passive Q-switched crystal (4), an output mirror (5), a beam splitter (6), a light detector (7) and a feedback device (8), wherein: the pump source (1), the coupling lens (2), the laser gain medium with a total reflection film (3), the passive Q-switched crystal (4), the output mirror (5) and the beam splitter (6) are arranged in sequence in an optically coaxial manner; the light detector (7) is arranged corresponding to the beam splitter (6) to monitor the light reflected by the beam splitter (6) in real time; the feedback device (8) is arranged between the light detector (7) and the pump source (1) and adjusts the power of the pump source (1) according to the detection result of the photoelectric detector (7); The pulse light delay feedback adjustment method comprises the following steps: ①, setting the low level of the pulse square wave of the pump source (1) to half of the low level leakage current, setting an appropriate duty cycle so that there is only one light pulse in one pump source pulse square wave, and setting an appropriate high level so that the light pulse is delayed by the desired time t relative to the rising edge of the pump square wave; ②, using a light detector (7) to detect the light wave signal reflected by the beam splitter (6), and using a feedback device (8) to compare the delay time of the light pulse tested in real time with the rising edge of the pump square wave with the expected value t, and when it is determined that the delay time becomes greater than t+△t, the low level of the pulse square wave of the pump source (1) is increased from a to b until the delay time returns to t; ③. Using a light detector (7) to detect the light wave signal reflected by the beam splitter (6), the delay time of the light pulse in real-time test relative to the rising edge of the pump square wave is compared with the expected value t through a feedback device (8). When it is determined that the delay time is reduced to t-△t, the low level of the pulse square wave of the pump source (1) is reduced from a to c until the delay time returns to t.

2. The pulse light delay feedback adjustment method of a pulse pumped passively Q-switched laser with a controllable light delay function according to claim 1, characterized in that: The pump source (1) adopts a pulse operation mode.

3. The pulse light delay feedback adjustment method of a pulse pumped passively Q-switched laser with a controllable light delay function according to claim 1, characterized in that: The pump source (1) is a semiconductor laser, and its wavelength range corresponds to the absorption peak of the laser gain medium (3) with a total reflection film.

4. The pulse light delay feedback adjustment method of a pulse pumped passively Q-switched laser with a controllable light delay function according to claim 1, characterized in that: The laser gain medium (3) with a total reflection film and the output mirror (5) form a resonant cavity.

5. The pulse light delay feedback adjustment method of a pulse pumped passively Q-switched laser with a controllable light delay function according to claim 1, characterized in that: The pump source (1) converges the pump light onto a laser gain medium (3) with a total reflection film through a coupling lens (2); the gain medium (3) absorbs the pump light and forms a population inversion, and the laser generates gain.

6. The pulse light delay feedback adjustment method of a pulse pumped passively Q-switched laser with a controllable light delay function according to claim 1, characterized in that: The passively tuned crystal (4) is a Q-switched crystal based on the saturable absorption characteristics of the crystal.

7. The pulse light delay feedback adjustment method of a pulse pumped passively Q-switched laser with a controllable light delay function according to claim 1, characterized in that: The beam splitter (6) has a partial reflection film for the output light.

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